Calibrator for radio echo system



Sept. 18, 1956 W. M. FAIRBANK CALIBRATOR FOR RADIO ECHO SYSTEM Filed Dec. 18, 1945 ATTENUATOR h 26 HIGH POWER SWITCH HKa-IF'PE Q RECEIVER 22 FIG. I

INVENTUR WILLIAM M. FAIRBANK ATTORNEY United States cALmRAToR non RADIO ncno SYSTEM William M. Fail-bank, New Haven, Conn, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application December 18, 1945, Serial No. 635,7t36

4 Claims. (Cl. 343-17.7)

This invention relates to apparatus for testing or checking the efiiciency of operation of a radar system, and for determining whether its transmitter or receiver is out of proper adjustment. The criterion applied is the power difference between the peak transmitted power and the minimum detectable signal.

The object of the invention is to provide a simple, easily installable apparatus for making such test without need of using additional extraneous oscillator, signal generator or other power consuming tubes for the testing purpose.

Fig. l is a diagram illustrating the principle of the invention and Fig. 2 is a section view of one type of wave guide switch which is a necessary component for convenient and effective employment of the invention.

The testing may be done in accordance with this invention by shutting off the transmitter from the main line by a highly effective blocking switch of some kind and then coupling a measured proportion of the transmitter power to the receiver through an attenuator which reduces the coupled signal to the minimum that can be detected by the receiver. The calibration of the attenuator will give the desired power ratio referred to above. By measuring the actual transmitter output at the same time it is possible to ascertain positively the operating efficiency of the transmitter and the receiver.

The measurement of the transmitter output power monitors the performance of the transmitting part of the radar system. This information plus the test with the calibrated attenuator gives an absolute check on the receiving system performance. The same principle applies to echo box testing. However, the present device is more accurate and is not critical with respect to frequency shifts caused by changes of temperature, tube replacements etc.

Referring now to Fig. 1 there is shown diagrammatically the arrangement of components in accordance with the invention. As in the usual radar system, there is indicated a transmitter or magnetron connected by the main wave guide 12 to the primary radiator 14 energizing a reflector 16 the latter items being a common antenna type. Also indicated are a conventional receiver protective transmit-receive switch 18 on the branch guide 20 leading to the radar receiver 22. Between the receiver branch guide 2% and the transmitter is shown a conventional anti-transmit-receive switch 24.

In addition there is provided a high power blocking switch 26 in the main line 12 with the transmitter on one side and the receiver and the antenna on the other. Also the transmitter itself should be provided with a complete shield 28 to prevent leakage of energy from the transmitter 10 to the receiver 22 except through a desired testing channel to be described. Likewise the blocking switch 26 in the main guide 12 should do as complete a blocking job as possible when testing is being done.

For the purpose of testing there is provided in accordance with the invention an auxiliary wave guide section or test section 30 coupled into the main guide 12 at 2,753,858 Fatented Sept. 18, 1956 point 32 on the transmitter side of the blocking switch 26 by any standard Wave selector or directional coupling methods and also provided with wave selector or directional coupling back into the main guide 12 at point 34 on the receiver side of the blocking switch 26.

On the main guide 12 near the transmitter a standard high power meter 36 is provided for measuring the transmitted power. In the test line 36 is inserted a previously calibrated variable attenuator 38.

The testing operation is asfollows. With the magnetron ltl properly shielded to prevent leakage and with the main line 12 blocked by switch 26 a definite known proportion of the transmitted power is directionally coupled into the test wave guide section 30, is reduced by being passed through a variable attenuator 38 which has been previously calibrated to indicate the ratio between input and output power thereof, and is then again directionally coupled back into the main guide 12 at point 34 to feed the receiver 22. The attenuation is increased until the minimum signal to which the receiver 22 will respond is being passed. The ratio of the transmitted power to the minimum receivable signal is thus obtained from the calibrated attenuator 38. Simultaneously the actual value of the transmitted power being put out by the magnetron Iii can be measured by any standard method as by meter 36. From these measurements and their comparison with previous tests, the performance is checked of the transmitter receiver and the associated plumbing so-called which includes the TR box 18, the wave guide 20 and a portion of the main wave guide 12.

The apparatus of this invention can be added to the original radar system with very little additional complication, no additional power ncr oscillator being needed. It is important, however, that the shielding of the transmitter and the shutting off by the switch be efficient to prevent any leakage of energy that can be detected by the receiver during testing. The switch 26 is designed also of course to present to the magnetron it the characteristic impedance of normal operation.

It may be noted that the directional couplers at points 32 and 34 are permament, non-adjustable components which serve two functions. They act to attenuate the transmitter output power very greatly so that the variable attenuator 38 need provide only a fine adjustment to be added to reduce the signal to the receiver threshold value. Also the directional coupling at point 34 rejects power normally coming in from the antenna 14- and so is prevented from bleeding away a large portion of normal incoming echo signals.

It should also be noted that in the testing operation the metered energy through the by-pass channel 30 has the same frequency as normal receiver signals because both are caused by the same transmitter. Also the metered energy'has the same pulse form as normal echo signal and it enters the receiver 22 plumbing 13 from the same direction as normal signals from the antenna 14 because of the directional coupling and its point of entry as with reference to the receiver 22. For instance, if otherwise directional coupling point 34 were between points 26 and 24, the system would not be operative.

Referring now to Fig. 2 there is shown in section one type of high power switch suitable for blocking the main line during the test which will satisfactorily perform the function of shutting off the high power efficiently and also of presenting the characteristic impedance of normal operation at the same time. The constructional details appear in the drawing. The box Gil containing the switch is constructed on the wave guide 52 with standard choke joints 53, 54, 55 and 56 at the junction points. Above and below these joints in the plane normal to the energy transmission, polyiron sections 58, 5%, 6t; and 61 are mounted in the box to absorb any energy that may leak around the edges of the: chokes at around the movabiei ing; the: energy :beiug: transfer-radio; tl eteeeiver said 21- I I myimn step shaped mer nber- 62 when raised intu :the tenuatur being r;atiia rartedI :fnr measuring the, retina of 1b,

p'pe'r es'i tion by a rcid 64 arid iutermediate: piunger 66 5 puwerinput 'tQ said attenuatcr tothe poweroutputthereufg; I for bteckingthe wave guide '52 egainst gasserg'e 0.5 energy i 2. In 1 combination, I an apparatus in accordance with thefeaio'ng. I 5 claim :1- andahighpower.meter'formeasuringthe actual The meta} plunger: 66; which :c'an; be moved 1 and: 1 i :pew r o p t f; sa d; ra m e wh r b it ma I 5 down by rod 64 cbn'tains' two openings} thmugh it whieh ajscertained whether? the. transmitter and the receiver: are: I wean be aii gued with the Wave guide 52. i (he. Qpening i ppraperly adjusted. I I v I I em; .1 I .1 r 68 is emptyanu of ithe same :eress section :as. the g i e I 3-; iAup m :fQr s ing: th e fi i ncyz of a rad r eye: I I I '52 so that :a; fcon'tiuueu's guide is provided: in this p qs'itien 10 tem; comprising a transmitter ands. receiver coupled; t9 (the one slatown= in the; figure-1. The other Open ng. 5 cummm :zmtennia; .by a conventinnal waye guii( c :r m contains the u'olyiro'n step 62 which fills the guide. :6. missien :l-ine; means for; blackingihe; passage of energy: mens'ions' :nbrm'aito energy transmissien and so: gcomstii from said transmitterthrqngir said transmission line, I an: 1 I tutes an open switch when: raised intn alignment with the i adjustable attenuator, Imeans for measuring the pews r guide 52 to serve its iailine termination or: short: circuit,: input: to said attenuator; a; test :path' inuluding said :at which presents the same impedance my the magnetrcm t im tate: =shunting;attenuated; energy from said trausm 3 :d the m and: antenna in ithe switch cicseci position. I I ter around said: mucking means; in said: receiver; where; Likewise? the step is: adapted =te :present; to the ather die I I by the adjustment of said: attenuatsr serves: tQ indie-ate: rectian the sameimpedance thatzwould ioceur in the post: i I the ratiei of :transm ittecl= power :to the rni,ni;m;ur;1 signal; 'tion cif nerma'l'nperation. I detectablebysaid'receiver.= In flie centerof the step 62 is a metai finflzmprevent :4; Apparatus. 011 I testing the :efiiciency: or a: :1: 111; energy of a: level detectable. by the receiver frompassing I I system; having a; ztreulsmgitter a receiver ;ceupled 1- through the switch Since the switch isetectricaily sym- I common: antenna by; a eqnventianal wa ve zguidemraus-z metrical; the fuuetitms are efieetive in both =directions.: f mission =1ine: including. conventional pmiectiive ide /ices; Whiie-a partieu larspecific embodimenthas been shown cumpriSing; a calibrated adjustabie attenuator, a test: patand -clescribedthe inventicm should be deemed limited f including saidiatte'rruator, means for: blOCiCing th jassage I o by the gpi it ofjthe' appendedf Iaims I uf energy from saidtra'nsmitter through-said transmission i 1 What 'i'sietaimed isi 2 I 2 line; directional; coupliug means for sampling said test 9 '1 In a 'riadar' system: having a transmitteri and: a: re-: I f path .into sa'id transmission fline: shunting said blocking I eiver :coup'led ts =a= main wave; guide; Ia test apparatus; means t0 coupie energy frorn'said transmitter: direetiy to f I for ascertaining the .r att-io :cif transmitted power; 2120 the a said; receives und means: t0= measure; the power: output minimum sign'al detectable by said receiver, ccmprisingif said transmitter .said caiihrated adjustable attenuator aihigh puv ve r switch, inserted near the transmitter: in the 2 serving to. indicate the ratio of; power input: to per I main wave :guide: for bloekingz passage of t transmitted i cutput of said attenuaton I I I I I e I I I I I I energy along the wave guide 3nd simultaneously present I I I 7 tingi to the transmitter aud ts the receiver the character- 1 'istic impedances of. Dermal: uperatiom a test a wave guide R ei feret estilitetil; the

' tor cooperating with pm'tmns 0f :s ard ma n gurdet tra-n 1 55125 i I fer energy from said transmitter to'saidf'ceivfi, and a i: Q I variable attenuator inserted in said test guide for reduc 2532539 Countel et 1950 

